The invention relates to titanium articles and structures for inspection methods and systems. In particular, the invention relates to inspecting titanium articles and structures using ultrasonic energy inspection methods and systems.
Nondestructive evaluation of articles and structures by ultrasonic inspection and ultrasonic inspection testing is a known testing and evaluation method. Ultrasonic testing typically requires that detectable flaws in the articles and structures possess different acoustic behaviors from bulk material articles and structures undergoing similar ultrasonic inspection. This different behavior permits the ultrasonic inspection to detect flaws, grains, imperfections, and other related microstructural characteristics for a material.
Materials forming articles and structures with large, elastically anisotropic grains, such as, but not limited to, cast ingots of steels, titanium alloys, and nickel alloys, are often difficult to evaluate by ultrasonic testing. The difficulties arise, at least in part to, because sound waves, which are used for ultrasonic inspection, are reflected from grains and grain arrays sharing common elastic behavior, and represent a background xe2x80x9cnoise.xe2x80x9d The generated background noise can mask flaws in the material, and is thus undesirable.
Ultrasonic inspection techniques have been developed that use focused ultrasonic beams to enhance a flaw fraction within any instantaneously insonified volume of material in articles and structures. These developed ultrasonic inspection techniques can identify indications based both on maximum signal, as well as signal to noise. A scattering of sound in a polycrystalline metallic material body, which is also known in the art as an attenuation of a propagating sound wave, can be described as a function of at least one of grain dimensions, intrinsic material characteristics, and ultrasound frequency. Typically, three different functional relationships among scattering, frequency, and grain dimensions have been described. These are:
for xcex greater than 2 xcfx80D, xcex1=Txcexd4"THgr"), termed xe2x80x9cRayleighxe2x80x9d scattering;
for xcex less than 2 xcfx80D or xcex≅D, xcex1=Dxcexd2xcexa3, termed xe2x80x9cstochasticxe2x80x9d or xe2x80x9cphasexe2x80x9d scattering; and
for xcex less than  less than D, xcex1xe2x88x9d1/D, termed xe2x80x9cdiffusionxe2x80x9d scattering;
where xcex1 is attenuation, xcexis wavelength of the ultrasound energy, xcexd is frequency of the ultrasound energy, D is an average grain diameter, T is a scattering volume of grains, and "THgr" and xcexa3 are scattering factors based on elastic properties of the material being inspected.
The microstructure of a material in articles and structures can determine the applications in which the articles and structures can be used, and the microstructure of a material can limit the applications in which the material can be used. The microstructure can be determined by measuring the scattering of sound in a material. The scattering of sound in a material, such as titanium, may be sensitive to its microstructure. The titanium microstructure""s sound scattering sensitivity can be attributed to xcex1Ti particles that are arranged into xe2x80x9ccolonies.xe2x80x9d These colonies typically have a common crystallographic (and elastic) orientation, and these colonies of xcex1Ti particles can behave as large grains in the titanium material. An individual xcex1Ti particle might be about 5 xcexcm in diameter, however, a colony of xcex1Ti particles could be greater than about 200 xcexcm in diameter. Thus, the size contribution attributed to sound scattering sensitivity from xcex1Ti particles could vary over 40-fold among differing microstructures. Additionally, the sound scattering sensitivity due to xcex1Ti particles could change between that from randomly crystallographically oriented xcex1Ti particles to that from xcex1Ti particles within crystallographically oriented colonies of xcex1Ti particles.
Colony structures are formed during cooling a titanium alloy from a high temperature as xcex2Ti transforms to xcex1Ti. There is a crystallographic relation between the xcex1Ti and the parent xcex2Ti grain, such that there are only three crystallographic orientations that xcex1Ti will take forming from a given xcex2Ti grain. If the cooling rate is high and there is uniform nucleation of xcex1Ti throughout the grain, neighboring xcex1Ti particles have different orientations, and each behave as a distinct acoustic scattering entity. However, if there are only a few sites of xcex1Ti nucleation within the xcex2Ti grain, then the xcex1Ti particles in a given area all grow with the same orientation, and a colony structure results. This colony becomes the acoustic entity. Since a colony is formed within a xcex2Ti grain, the colony size will be less than the xcex2Ti grain size. The size of xcex2Ti grains and the nature of xcex1Ti particles colony structures may be important variables that influence ultrasonic noise and ultrasonic inspection in single phase and two-phase titanium alloys and materials. Therefore, the size of xcex2Ti grains and the nature of xcex1Ti particles in colony structures may influence ultrasonic inspection techniques, methods, and results by creating undesirable noise during ultrasonic inspection. While thermomechanical processing techniques, which rely on dynamic recrystallization in the xcex1+xcex2 temperature range to achieve uniform fine grain (UFG) xcex1Ti particles and prevent colony formation, have been developed to improve titanium microstructure, defects may remain in the titanium material. These defects may be undesirable for some titanium material applications.
While ultrasonic inspection of most articles can be preformed with some degree of certainty, the shape, size, configuration, structure, and orientation of the articles and structures undergoing ultrasonic inspection may impair the ultrasonic inspection. There are shapes, sizes, configurations, structures, and orientations of some articles and structures that may enhance the ultrasonic inspection. Thus, in order to have acceptable titanium for certain applications, it is desirable to provide titanium articles and structures for ultrasonic inspection that enhances the ultrasonic inspection and can assist in the determination and differentiation of noise during ultrasonic inspection. Thus, with certain titanium articles and structures ultrasonic inspection method should be able to determine if ultrasonic inspection noise is attributed to a defect in the titanium material, or is due to other factors.
Therefore, a need exists for providing titanium articles and structures for ultrasonic inspection methods for enhancing accurate determinations of material characteristics and properties. Further, a need exists for providing titanium articles and structures for ultrasonic inspection for enhancing accurate determinations of processed titanium characteristics and properties.
In one aspect of the invention, a titanium article for an ultrasonic inspection is provided. The titanium article can be ultrasonically inspected for determining its acceptability in for microstructurally sensitive applications. The ultrasonic inspection method comprises providing a titanium article, directing ultrasonic energy of ultrasonic inspection to the titanium article; scattering reflected energy in the titanium article; determining an amount of noise generated by the ultrasonic inspection of the titanium article; and characterizing the titanium article as acceptable if the amount of noise as a function of ultrasonic frequency or wavelength is characteristic of predominantly Rayleigh scattering, which means that the Rayleigh scattering comprises at least a majority of the scattering and dominates other types of scattering, and the magnitude of the noise is less than a pre-determined noise level. The titanium article comprises an uniform-fine grain microstructure. The uniform-fine grain microstructure generates predominantly Rayleigh scattering when undergoing ultrasonic inspection.
The invention also sets forth a method for forming a titanium article for an ultrasonic inspection. The ultrasonic inspection method is capable of determining acceptability of the titanium article for microstructurally sensitive applications in which the method comprises providing a titanium article, directing ultrasonic energy of ultrasonic inspection to the titanium article; scattering reflected energy in the titanium article; determining an amount of noise generated by the ultrasonic inspection of the titanium article; and characterizing the titanium article as acceptable if the amount of noise as a function of ultrasonic frequency or wavelength is characteristic of predominantly Rayleigh scattering and the magnitude of the noise is less than a pre-determined noise level. The method of forming comprises providing a uniform fine grain titanium material by a processes selected from forging and heat treating a billet of conventional titanium material into the titanium article.